Funnily, I’ve just been answering some posts about MIDI on another forum.
MIDI is a couple of things but, at it’s heart, is a format for representing music in a way that’s separate from the actual sound.
MIDI represents music as events. Specifically, note on events which indicate the start of a note, and note off events which indicate the end of a note. These correspond with pressing and releasing a key on a synthesizer keyboard.
Each event has a note value which says which pitch to play the note at. The format (generally) contains almost no information about what sound should be played for each note.
So you could record a MIDI sequence on a keyboard into a DAW, and play it back through an instrument plugin. You could record it using a piano sound, but play it back using a timpani, or a recording of a dog bark, or a church organ, etc.
MIDI takes, roughly, two forms: the real-time data being transmitted down wires between instruments as part of a live performance (or a playback of a live performance) and a data file on a computer. Both are, basically, the same thing but one is encapsulated in a file so you can copy it, send it by email, etc. and the file includes the timing information (when each event occurred).
You can then use a MIDI application to play back the MIDI file into a software instrument, or via a MIDI interface to a hardware MIDI synth and it will play back the song.
You can also use MIDI editors in DAWs and other tools (Guitar Pro, MuseScore, Tuxguitar, etc.) to create compositions from scratch or to edit existing MIDI files.
MIDI doesn’t just do notes: it can also store pitch bend, modulation, note velocity, aftertouch, and a host of other music performance information.
It allows you to play that file using any MIDI instrument (hardware or software) or to copy that file to somewhere else, like a DAW to use as part of a composition.
For instance, you could create a Tab in MuseScore, export it as MIDI, import it into a DAW, select an instrument, and then it could be part of your composition, such as a bassline or drum track.
The important thing to understand is that MIDI itself doesn’t make any sound. A MIDI file needs a MIDI instrument to interpret the note and other data and to make appropriate sounds.
Most TAB editors have a built in MIDI player for your convenience.
I hope this makes sense.